<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        function SuperType() {
            this.property = true;
        }

        function SuperType() {
            this.property = true;
        }
        SubType.prototype.getSubValue = function() {
            return this.subproperty;
        };
        var instance = new SubType();
        alert(instance.getSuperValue()); //true
    </script>
</body>

</html>